Many lawn mowers are known which comprise a self-propelled traction unit of some type, such as the frame of a riding mower. Many of these mowers carry a multi-bladed rotary cutting deck having a plurality of blades that rotate in substantially horizontal cutting planes to cut grass over a relatively wide swath as the mower makes a single pass over the ground. Such cutting decks often utilize three cutting blades arranged in a staggered configuration comprising a forward central cutting blade flanked on each side by trailing side cutting blades. Such a fore-and-aft staggered configuration allows the deck to cut an unbroken swath of grass during forward motion of the mower without there being any danger of the blades hitting one another.
In many cases, such multi-bladed cutting decks have used cutting blades that are the same as each other and that rotate in the same direction, i.e. all towards the left side of the deck or the right side of the deck. In many cases, such decks have had a discharge opening arranged on the side of the deck towards which the clippings were directed by the blades to allow the clippings to be thrown outwardly past the side of the deck. However, such a blade arrangement does not work well in a rear discharge deck where one desires that the clippings be thrown out to the rear of the deck through a rear discharge opening. In such a case, the unidirectional rotation of all the cutting blades causes the grass clippings to be thrown out to the rear in a windrow along one side of the deck. This is not aesthetically pleasing and additionally prevents the grass clippings from breaking down into mulch as quickly as they would have broken down had such clippings been more evenly distributed over the cut grass swath.
Various attempts have been made to improve the distribution of clippings to the rear when a rear discharge opening is provided on a mower deck. However, many such attempts have embodied fairly complicated baffling structure on the underside of the mower deck to create entirely separate flow paths for the grass clipping streams generated by the various cutting blades. While this may in some cases cause a more even distribution of clippings, the cost of extensive baffling can be expensive to manufacture and maintain. More significantly, the presence of the baffling can affect how well the cutting blades cut the grass in the first place, as unevenly cut streaks of grass might appear along the lines of the baffling or elsewhere. Thus, there is a need in the art for a rear discharge mower deck that accomplishes a more even and uniform distribution of grass clippings across the width of a rear discharge opening while maintaining a high quality of cut.